I would have liked a little more detail in the fan/filter trade off section.
It's not entirely true that you need a loud fan to move more air through a filter. That looks like a duct booster fan in the picture. Those have very weak (and usually inefficient) motors and impeller design. You could use a PSC motor running a squirrel cage fan. PSC motors are efficient and can handle higher torque. The torque can be used with an appropriate fan/impeller design (like a squirrel cage) to handle the pressure drop through the filters.
That said, the duct boosters are cheap and readily available. Here's a homemade hybrid flow/glove box for inoculating mushroom substrate.
The article does address the type of fan and tradeoffs:
> An 8inch (20.32cm) diameter inline duct booster fan ($30).
> Inline duct booster fans are fairly weak fans often
> used to help with grow rooms or range hoods. An inline
> duct fan would probably perform even better (see the
> discussion) but at a higher cost. The one I bought
> is rated to push around 12 m³ of air per minute.
Yeah, but they didn't really go into fan efficiency with pressure drops or motor efficiency.
One other thing is longevity and even safety. Maybe their use of multiple filters reduces the pressure enough. But if it doesn't, then the motor will wear out pretty quickly and could potentially start a fire if it's generating enough heat. The motor in my setup gets pretty hot when running at full power.
It's not entirely true that you need a loud fan to move more air through a filter. That looks like a duct booster fan in the picture. Those have very weak (and usually inefficient) motors and impeller design. You could use a PSC motor running a squirrel cage fan. PSC motors are efficient and can handle higher torque. The torque can be used with an appropriate fan/impeller design (like a squirrel cage) to handle the pressure drop through the filters.
That said, the duct boosters are cheap and readily available. Here's a homemade hybrid flow/glove box for inoculating mushroom substrate.
https://postimg.cc/NKrGGRFH